Conventionally positioners, which are field devices that control the degrees of opening of regulator valves, are designed so as to operate with an electric current between 4 and 20 mA sent through a pair of electric wires from a higher-level system. For example, if a current of 4 mA is sent from the higher-level system, the valve opening of the regulator valve is set to 0%, and if a current of 20 mA is sent, then the valve opening of the regulator valve is set to 100%.
In recent years there have been proposals for positioners that have, in addition to their actual functions of controlling the degree of opening of the regulator valves, also opening degree transmitting functions, regulator valve fault diagnostics, and functions for sending, to the higher-level system, the results of fault self-diagnostics, and the like (See, for example, Japanese Unexamined Patent Application Publication H1-141202).
FIG. 6 is a shows a structural diagram of the critical components in a positioner that has a conventional communication function. In this figure, 1 is a positioner, 2 is a higher-level system, and 3 is a regulator valve. The positioner 1 is connected by two double-wire transmission paths to the higher-level system, and is provided with an input signal detecting portion 12, a valve lift detecting portion 13, a calculation processing portion (CPU) 14, an electro-pneumatic converting portion 15, an A/D converting portion 16, and a communication processing portion (electric current outputting circuit) 17.
The first double-wire communication path (first communication path) is a double-wire communication path 5 and 6 that is connected to a controller 4 of the higher-level system 2, where an electric current signal of between 4 and 20 mA, depending on the opening setting for the regulator valve 3, is inputted into the input signal detecting portion 12 of the positioner 1 from the controller 4 through this double-wire transmission path 5 and 6.
The input signal detecting portion 12 not only produces the operating power supply for the internal circuitry in the positioner 1 from the electric current signal of between 4 and 20 mA that is sent through the double-wire transmission path 5 and 6, but also sends a voltage signal, depending on the value of the electric current signal, to the A/D converting portion 16. The A/D converting portion 16 converts the voltage signal, from the input signal detecting portion 12, into a digital signal, and sends it to the calculation processing portion 14 as a signal indicating the opening setting for the regulator valve 3.
Note that the operating power supply produced by the input signal detecting portion 12 is provided to the internal circuitry, except for in the communication processing portion 17 of the positioner 1, through a switch SW1. In the present example, it is sent to the valve lift detecting portion 13, the calculation processing portion 14, the electro-pneumatic converting portion 15, and the A/D converting portion 16, as the internal circuitry that excludes the communication processing portion 17.
On the other hand, the valve lift detecting portion 13 detects the actual degree of opening of the regulator valve 3, and sends, to the A/D converting portion 16, a voltage signal in accordance with the actual degree of opening. The A/D converting portion 16 converts into a digital signal the voltage signal from the valve lift detecting portion 13, and sends it to the calculation processing portion 14 as a signal that indicates the actual degree of opening of the regulator valve 3.
The calculation processing portion 14, based on the signal indicating the opening setting of the regulator valve 3, and the signal indicating the actual degree of opening, sent through the A/D converting portion 16, generates a PWM signal in accordance with the deviation between the actual degree of opening and the opening setting for the regulator valve 3, and outputs it to the electro-pneumatic converting portion 15. The electro-pneumatic converting portion 15 converts the PWM signal, from the calculation processing portion 14, into a pneumatic pressure signal, and provides this converted pneumatic pressure signal to the driving portion of the regulator valve 3. As a result, the degree of valve opening (the valve lift position) of the regulator valve 3 is adjusted so that the actual degree of opening of the regulator valve 3 will match the opening setting.
Moreover, the calculation processing portion 14 has, in addition to the function for controlling the degree of opening of the regulator valve 3 in this way, also functions for calculating the actual degree of opening of the regulator valve 3, and functions for performing fault diagnostics on the regulator valve 3 and fault diagnostics on the positioner 1 itself.
The second double-wire transmission path (second transmission path) is a double-wire transmission path 7 and 8 that is connected to an external power supply 9 through a resistor 10, where the calculation processing portion 14 is connected through the double-wire transmission path 7 and 8 and the communication processing portion 17. The communication processing portion 17 operates based on the power supply that is provided, sent through the double-wire transmission path 7 and 8. This enables communication between the communicating device 11 and the positioner 1, which are connected to the double-wire transmission path 7 and 8, that is, enables transmission and reception of signals between the communication processing portion 17 and the communicating device 11. In an example of this, the actual degree of opening of the regulator valve 3, calculated by the calculation processing portion 14, the result of fault diagnostics for the regulator valve 3, or the result of self-diagnostics for the positioner 1 itself are sent from the communication processing portion 17 to the communicating device 11 on the outside.
As illustrated in FIG. 7, in a positioner 1 having this type of communication function, isolating circuits 18 are provided between the calculation processing portion 14 and the communication processing portion 17 to ensure electrical isolation of the inputs and outputs of the calculation processing portion 14 and the communication processing portion 17, so that no noise will be produced that would affect the processing operations in the calculation processing portion 14 or the communicating device 11.
FIG. 8 illustrates one example of an isolating circuit 19 that is provided in the transmission path from the calculation processing portion 14 to the communication processing portion 17. This isolating circuit 19 is illustrated as a pulse train signal transmitting device in Japanese Publication of Examined Application H6-48827 (“JP '827”). Note that an isolating circuit 20 is provided similarly in the transmission path from the communication processing portion 17 to the calculation processing portion 14.
In FIG. 8, 191 is an exclusive OR circuit, 192 is a photocoupler, 193 is a flip-flop, R1 through R5 are resistances, D1 is a diode, C1 and C2 are capacitors, T1 is an input terminal for a signal a from the calculation processing portion 14, and T2 is an output terminal for a signal e to the communication processing portion 17.
FIG. 9 is a timing chart illustrating the operation of the isolating circuit 19. FIG. 9 (a) is a signal a from the calculation processing portion 14 (one input signal into the exclusive OR circuit 191), (b) is an input signal b into the other input of the exclusive OR circuit 191, (c) is an output signal c of the exclusive OR circuit 191 (the input signal into the reset terminal of the flip-flop 193), (d) is an integrating signal d (the input signal into the set terminal of the flip-flop 193), and (e) is a signal e to the communication processing portion 17 (the Q output of the flip-flop 193).
When a pulse train signal is sent as the signal a from the calculation processing portion 14, the isolating circuit 19 produces a wide edge signal c as the output signal c of the exclusive OR circuit 191 on the rising edges of the pulse train signal, and produces a narrow edge signal c on the falling edges of the pulse train signal. Given this, the edge signal c that is produced is reproduced as a transmission signal c by the photocoupler 192, and this transmission signal c is inputted into the reset terminal of the flip-flop 193 while, at the same time, it is inputted into the set terminal of the flip-flop 193 as the integrating signal d that is inputted into the integrating circuit that is structured by the resistance R5 and the capacitor C2. As a result, the flip-flop 193 is repetitively set and reset, producing a signal e that reproduces the input signal a as the Q output of the flip-flop 193, where this signal e, which reproduces the input signal a, is sent to the communication processing portion 17.
The calculating processing portion 14, when sending the actual degree of opening of the regulator valve 3 to the communicating device 11, uses a pulse train signal having a duty ratio in accordance with the actual degree of opening as the signal a to the isolating circuit 19. The communication processing portion 17 receives the pulse train signal from the calculation processing portion 14 and adjusts the electric current that is outputted to the double-wire transmission path 7 and 8 to an electric current in the range of between 4 and 20 mA. Moreover, the calculation processing portion 14 has a function for performing fault diagnostics on the regulator valve 3 and a function for performing fault diagnostics on the positioner 1 itself, and when a fault is identified, a signal of a level that is different from the normal electric current range of between 4 and 20 mA is outputted to the double-wire transmission path 7 and 8 as a burnout signal (a warning signal).
This burnout signal has a burnout H signal of a level that is higher than the upper limit value of the normal electric current range, and a burnout L signal of a level that is lower than the lower limit value of the normal electric current range, and one of these burnout signals is set in advance as an output signal for when a fault is identified. For example, if the communicating device 11 is a device that recognizes a signal of a level that is higher than the upper limit value of the normal electric current range as being a fault, then the calculation processing portion 14 is set up to output the burnout H signal as the warning signal. In this case, the Q output of the flip-flop 193 in the isolating circuit 19 is caused to maintain a “H” level (a voltage level indicating the burnout H signal) through a command from the calculation processing portion 14. If the communicating device 11 is a device that recognizes a signal of a level that is lower than the lower limit value of the normal electric current range as being a fault, then the calculation processing portion 14 is set up to output the burnout L signal as the warning signal. In this case, the Q output of the flip-flop 193 in the isolating circuit 19 is caused to maintain a “L” level (a voltage level indicating the burnout L signal) through a command from the calculation processing portion 14.
In the positioner 1 illustrated in FIG. 7, the operating power supply is obtained from the double-wire transmission path that is different from that of the calculation processing portion 14 and the communication processing portion 17, making it possible to produce independent power supply ON/OFF states. For example, if the operator forgets to turn ON the switch SW1 that makes it possible to provide power to the internal circuitry of the positioner 1, then a fault status may occur wherein the power supply to the calculation processing portion 14 may be turned OFF notwithstanding the power supply to the communication processing portion 17 being in the ON state. In this case, the fault status cannot be detected by the external communicating device 11, and so there is the potential for a problem wherein the positioner 1 may be left in the fault state for an extended period of time.
This problem is explained in more detail below. If the power supply to the calculation processing portion 14 goes into the OFF state while the power supply to the communication processing portion 17 is in the ON state, then the Q output of the flip-flop 193 in the isolating circuit 19 may either go to a constant “H” level or a constant “L” level.
In this case, even though it is possible for the communicating device 11 to identify the fault state of the positioner 1 when the burnout H signal is the output signal when a fault is detected, and the Q output of the flip-flop 193 is constant at the “H” level, it is not possible for the communicating device 11 to recognize the fault state of the positioner 1 if the Q output of the flip-flop 193 is constant at the “L” level.
Conversely, even though it is possible for the communicating device 11 to identify the fault state of the positioner 1 when the burnout L signal is the output signal when a fault is detected, and the Q output of the flip-flop 193 is constant at the “L” level, it is not possible for the communicating device 11 to recognize the fault state of the positioner 1 if the Q output of the flip-flop 193 is constant at the “H” level.
In this way, if, when the power supply to the communication processing portion 17 is ON the power supply to the calculation processing portion 14 is turned OFF, the level of the Q output of the flip-flop 193 in the isolating circuit 19 cannot be defined uniquely, making it impossible to send a burnout signal reliably to the communicating device 11 in a direction that can be identified by the communicating device 11, so there is the risk of a problem in that the positioner 1 may be left in a fault state for an extended period of time.
The examples of the present invention solve problem areas such as these, and the object thereof is to provide a field device wherein it is possible to provide a fault state notification reliably to the outside when a power supply to a calculation processing portion goes OFF while a power supply to a communication processing portion is in the ON state.